This invention relates to rapid thermal processing of a workpiece and more particularly relates to thermal processing of semiconductor wafers.
Rapid thermal processing reactors are commonly used to anneal semiconductor wafers. The operating parameters for these reactors are becoming more demanding as device spacing on semiconductor wafers is reduced. For example high temperature rapid thermal processing for devices with 0.25 .mu.m spacings requires a temperature uniformity in the device of .+-.3 degrees celsius and for devices with 0.18 .mu.m spacings a temperature uniformity of .+-.1 degree celsius is required.
Various others have attempted to uniformly irradiate a semiconductor wafer for using devices as described in U.S. Pat. No. 4,649,261 issued Mar. 10, 1987, to Sheets, U.S. Pat. No. 5,279,973 issued Jan. 18, 1994, to Suizu, U.S. Pat. No. 4,482,393 issued Nov. 13, 1984, to Nishiyama et al., U.S. Pat. No. 5,155,336 issued Oct. 13, 1992, to Gronet et at., U.S. Pat. No. 4,981,815 issued Jan. 1, 1991, to Kakoschke and U.S. Pat. No. 4,958,061 issued Sep. 18, 1990, to Wakabayashi et al. Generally, each of the references above discloses at least one light source and various reflector arrangements for directing at the semiconductor wafer light produced by the light source. Using conventional light sources, often a plurality of light sources are required and efficient use must be made of reflectors in order to achieve required radiation pattern on the wafter to achieve a desired thermal pattern in the wafer. The design of such reflectors and, in general, irradiating systems of the type described in the patents, normally are required to compensate for reflection, emission and absorption effects of the wafer itself. This is because the wafer can reflect and emit radiation which is reflected from various reflecting surfaces in the chamber back at the wafer, thereby creating local hot spots in the wafer. Furthermore, differences in geometry and thermal properties of various areas on the wafer can complicate the emissive, absorptive and reflective effects further contributing to localized hot spots in the wafer.
What would be desirable, therefore, is a system which uniformly irradiates the wafer and reduces the effects of radiation absorbed and reflected by the wafer. By reducing these effects, the required temperature uniformity for devices with spacings less than 1 .mu.m can be achieved.